Will this for loop run infinitely?

Question

I have some experience with the c programming but sometimes the author of some books just pose such strange syntactical question which we will never use in actual programming and similar to that I stuck on one such question though the answer is given but I am not able to understand the answer.Here is the code below

int main
{
int i;
for(;scanf("%d",&i);printf("%d",i)){
     ;
    }
}

The question is how many times this for loop will run and the answer given is indefinite Can anyone explain how the loop will get executed

Answer 1

scanf returns number of elements successfully read and in this case it will be 1 if it reads a integer and keeps printing it.

Let's say you pass a character here then scanf() fails and exits from a for loop